The present invention relates to a device and method for lighting of streets, open and large spaces and, more particularly, but not exclusively to a way of inserting newer energy efficient lighting technologies into legacy street lighting systems.
Legacy street lighting systems are based on high pressure discharge lamps, most commonly high pressure sodium (HPS) lamps. These have been generally recognized to give the highest amount of lighting per watt of electricity used.
In some countries, notably the UK, low pressure sodium (LPS) lamps are still widely used.
When scotopic/photopic S/P light calculations are used, it can been seen how inappropriate high pressure sodium lamps are for night lighting. White light sources have been shown to double driver peripheral vision and increase driver brake reaction time at least 25%.
New street lighting technologies, such as Light Emitting Diode (LED) and Induction lighting, emit a white light that provides high levels of scotopic lumens allowing street lights with lower wattages and lower photopic lumens to replace existing street lights.
However, a disadvantage with LED is that a sufficient surface area to provide the required illumination means that the LED lamp cannot be retrofitted into legacy light fittings.
Specifically, the fittings for sodium lamps are screw fittings, requiring the lamp to be inserted into the fitting and then rotated. An LED lamp of the required brightness will generally fit into the space of the fitting but cannot then be rotated for insertion into the screw fitting. Furthermore the space is filled with the LED lamp and supporting electronics to such an extent that cooling is insufficient. In general about half of the energy supply to the LEDs ends up as heat, and the space within the light fitting simply does not allow for so much heat. In particular the light fittings are generally closed, if not sealed, against the weather. If sophisticated heat dispersion mechanisms are provided these reduce the lifetime of the LED lamp. Hence, replacement of traditional street lamps with LED lamps requires either supplying an LED lamp that is too small to provide the requisite illumination or the rather expensive changing of the light fittings.